I compiled and ran your modification on an 18F452, and everything was fine.

Except that it was running at the wrong speed because the "osc" wasn't capitalized. changed it to...

DEFINE OSC 8

2.When I try to compile this code , I have error: "ReEnterPBP-18.pbp"
"Elapsed_INT-18.bas" not found. When I change BAS to PBP it is OK.
Why?
Please, help.
Browsers and webservers don't like files with a .bas extension, so on the website they are given a .txt extension to allow easy download. It's up to you to rename it to something usable such as .bas or .pbp. Then you have to use the same extention in your INCLUDE statements.